Correspondence, research notes, notebooks, scrapbooks, and other papers relating chiefly to Nicolay's public career particularly his tenure as secretary to President Abraham Lincoln and to his numerous literary activities including his works on Lincoln. Also documents his service as U.S. consul, Paris, France, and U.S. Supreme Court marshal. Includes papers of his daughter, Helen Nicolay. Correspondents include John Bigelow, Anson Burlingame, Simon Cameron, Schuyler Colfax, Roscoe Conkling, William Dennison, John A. Dix, James Dixon, George Gilman Fogg, Horace Greeley, James Tracy Hale, James Harlan, O.M. Hatch, John Hay, Robert Todd Lincoln, Alexander K. McClure, Joseph Medill, Edwin D. Morgan, Charles H. Philbrick, Whitelaw Reid, Carl Schurz, Charles Sumner, Leonard Swett, Theodore Tilton, Horace White, A.C. Woolfolk, and Nicolay's wife, Therena Bates Nicolay.